A belt continuously variable transmission in which the rotation speed of an input shaft connected to a drive source is varied continuously and transmitted to an output shaft is known. A belt continuously variable transmission is constituted by a primary pulley, a secondary pulley, and a belt wrapped around the two pulleys, and by varying the width of the two pulleys using oil pressure, the radius of contact between the belt and pulleys is varied, leading to variation in the speed ratio. JP2000-02322β published by the Japan Patent Office in 2000 discloses control of the speed ratio in terms of feedback control to align the actual speed ratio with a target speed ratio corresponding to driving conditions.